Method of effecting exothermic reactions



United States Patent Raymond S. Richards, Toledo, Ghio, HSSifiGZ to Qwens- Illinois Glass Company, a corporation of Ohio No Drawing. Filed Oct. 13, 1959, Ser. No. 84-80% 6 Claims. (Cl. 75-170) This invention relates to a method of effecting certain exothermic reactions. In particular, the invention relates to a method of preparing intermetallic compounds by the co-reaction of the elemental metals, during which co-reaction large amounts of heat are evolved.

There are a number of intermetallic compounds which are dangerous and impractical to prepare because of the highly exothermic nature of their formation. For instance, when forming the compound nickel aluminide, MA], by addition of one metal to a pool of the other molten metal, no reaction takes place at least to any appreciable extent, until substantially equivalent quantities of each metal are present. Then when the entire mass of molten metals has reached the stoichiometric ratio of substantially one atom of nickel for one atom of aluminum, the reaction suddenly initiates throughout the reaction mass with explosive violence, giving oif great quantitles of heat and actually vaporizing most of the metal. In order to overcome this problem, nickel aluminide is now commercially made by the tedious and expensive method of mixing powders of the two metals in the proper proportions and then carefully heating the mixture at relatively low temperatures for a day or longer, thus limiting the rate of reaction in order to avoid an explosively violent reaction. The nickel aluminide so made currently costs in excess of $11.00 per pound.

It is an object of the invention, therefore, to provide a method for forming intermetallic compounds at reasonable rates of reaction while at the same time avoiding the explosively Violent reactions of the prior art.

Other objects as well as advantages of the present invention will become apparent from the following description of the invention.

According to the invention there is provided a method for reacting a plurality of metals together to form an intermetallic compound which comprises the steps of providing an initially shallow pool of the mixed metals in the equivalent ratios for producing the desired intermetallic compound, and gradually adding portions of each of said metals to the surface of the pool at the same point or area on the surface of the pool, each of said metals being added at relative rates so as to maintain ratios of said metals during said addition substantially as before set forth, the rates of addition of said metals being maintained within a range such that substantially all melting of the added metals occurs substantially at the surface of said pool.

One way by which the process of the invention can be effected is to twist wires of the respective metals together, the diameters of the wires being chosen so that each linear increment of the composite twisted Wires contains the proper ratios of each metal. The end of the composite wire is then inserted in a heated crucible until a small pool of the mixed metals has formed and thereafter the composite twisted wire is inserted at a rate which assures that it will continue to be melted at the surface and will not extend unmelted to an appreciable extent below the surface of the pool. This method has proved to be extremely successful and has avoided the formation of metal vapors below the surface of the pool with consequent blowing out of the remaining liquid metal in the pool. Thus, the constant addition to the liquid pool of the solid, cold metals takes up a great deal of the exothermic heat of reaction by the absorbed heat of fusion involved in melting of the metal and also the sensible heat necessary to raise the metals to melting temperature and to reaction temperature. In the method of the invention, depending upon the particular reaction bein carried out, a small amount of heat can be continuously added or extracted from the reacting mixture by indirect heat exchange or even radiation in order to keep the reaction temperature at a desired constant value.

The method of the invention is applicable to any intermetallic compound made from two or more metals and is, of course, of greatest value to such compounds which are highly exothermic in their formation. In addition to nickel aluminide, other examples of compounds which can be made according to the present invention method from the respective elements include Fe Al, Al Ca, Al Ca B33812, BazPb, Bagsbz, Blzcaa, Ca Sb Case, Ca Sn, and K Se.

The nickel aluminide compound produced according to the present method is, for instance, particularly useful because of its high temperature resistance and its resistance to oxidation in air at high temperature, as is well known in the art.

Besides the twisted wire embodiment described hereinbefore, any other methods can be employed to provide for gradual addition of the metals in the proper ratio to the surface of the pool of liquid metals. Thus, Wires of each of the metals to be reacted of uniform diameter can be inserted at approximately the same place into the top of the pool of liquid at proper rates to maintain their ratio substantially in equivalent weights for preparation of the desired compound. Further, :dat strips of each of the metals can be twisted together instead of wires or flat strips can be inserted at relative rates in the same manner as described with respect to the wires without twisting together. Further, when one metal cannot be made into a wire or other cohesive elongated shape, the other metal can be formed in the form of a tube and the tube can be packed internally with the proper amount of the other metal in powder or other form so that the addition of the packed tube results in the addition of each metal in the proper ratio. Other specific methods can obviously be thought of in View of the foregoing teachings.

In a specific example of the invention the intermetallic compound nickel aluminide was prepared by twisting together wires of nickel and aluminum of 0.091 inch diameter and 0.113 inch diameter, respectively, and initially heating and melting a small portion of the combined metals in the proper proportion in a graphite crucible equipped with an induction heating coil. Thereafter, the twisted wires were inserted into the pool of molten metals at a rapid rate. The reaction was quickly eflected and a total of about 30 grams of the combined twisted metals were inserted into the top of the pool of liquid over a period of about 2 seconds. After addition of the twisted Wires was discontinued, the mass of nickel aluminide was allowed to cool. No trouble occurred with vaporization and blowing out of metal during the preparation.

As will be evident to those skilled in the art, various modifications of this invention can be made or followed in the light of the foregoing disclosure and discussion without departing from the spirit or scope of the disclosure or from the scope of the claims.

I claim:

1. A method for co-reacting a plurality of molten elemental metals to form an intermetallic compound of said metals while minimizing temperature rise of the reaction mass because of heat of reaction, which comprises gradually adding portions of each of said metals as separate solids to the surface of an initially shallow molten pool of said metals at substantially the same area of the surface of said pool said molten metals in said pool being in the stoichiometric proportions for formation of the desired intermetallic compound, each of the metals being added at relative rates such that the relative proportions of said metals are maintained in substantially stoichiometric proportions for formation of said intermetallic compound, the rates of addition of said metals being maintained within a range such that all melting of the added metals occurs substantially at the surface of said pool, said co-reacting proceeding during said gradual adding of said portions.

2. A method according to claim 1 wherein said intermetallic compound is selected from the group consisting of FegAl, Al Ca, Al Ca Ba Bi BazPb, Ba3sbz, Bigcag, Ca sb CaSe, Ca Sn, K Se and NiAl.

3. A method according to claim 1 wherein said compound is NiAl.

4'. A method for co-reacting a plurality of molten elemental metals to form an intermetallic compound of said metals while minimizing temperature rise of the reaction mass because of heat of reaction, which comprises forming a molten body of said intermetallic compound wherein said molten metals in said body are in the stoichiometric proportions for formation ofthe desired intermetalliccompound, gradually adding portions of each of said metals as separate solids to the surface of said molten body at substantially the same area of the surface of said molten body, each of said metals being added at relative rates such that the relative proportions of said metals are maintained in substantially stoichiometric proportions for formation of said intermetallic compound, the rates of addition of said metals being maintained within a range such that all melting of the added metals occurs substantially at the surface of said molten body, said co-reacting proceeding during said gradual adding of said portions. 5. A method according to claim 4 wherein said intermetallic compound is selected from the group consisting of F63Al, Al Ca, Al Ca Ba Bi Ba Pb, Ba Sb Bi Ca Ca Sb CaSe, Ca Sn, K Se and NiAl.

- 6. A method according to claim 4 wherein said compound is NiAl and said metals added to said molten body are in the form of a nickel wire and an aluminum wire.

References Cited in the file of this patent UNITED STATES PATENTS 702,996 Pruszkowski June 24, 1902 2,595,292 Reece May 6, 1952 2,677,609 Moore et al May 4, 1954 2,898,249 Jensen Aug. 4, 1959 2,910,366 Grada et al. Oct. 27, 1959 

1. A METHOD FOR CO-REACTING A PLURALITY OF MOLTEN ELEMENTAL METALS TO FORM AN INTERMETALLIC COMPOUND OF SAID METALS WHILE MINIMIZING TEMPERATURE RISE OF THE REACTION MASS BECAUSE OF HEAT OF REACTION, WHICH COMPRISES GRADUALLY ADDING PORTIONS OF EACH OF SAID METALS AS SEPARATE SOLIDS TO THE SURFACE OF AN INITIALLY SHALLOW MOLTEN POOL OF SAID METALS AT SUBSTANTIALLY THE SAME AREA OF THE SURFACE OF SAID POOL SAID MOLTEN METALS IN SAID POOL BEING IN THE STOICHIOMETRIC PROPORTIONS FOR FORMATION OF THE DESIRED INTERMETALLIC COMPOUND, EACH OF THE METALS BEING ADDED AT RELATIVE RATES SUCH THAT THE RELATIVE PROPORTIONS OF SAID METAL ARE MAINTAINED IN SUBSTANTIALLY STOICHIOMETRIC PROPORTIONS FOR FORMATION OF SAID INTERMETALLIC COMPOUND, THE RATES OF ADDITION OF SAID METALS BEING MAINTAINED WITHIN RANGE SUCH THAT ALL MELTING OF THE ADDED METALS OCCURS SUBSTANTIALLY AT THE SURFACE OF SAID POOL, SAID CO-REACTING PROCEEDING DURING SAID GRADUAL ADDING OF SAID PORTIONS.
 2. A METHOD ACCORDING TO CLAIM 1 WHEREIN SAID INTERMETALLIC COMPOUND IS SELECTED FROM THE GROUP CONSISTING OF FE3AL, AL3CA, AL5CA2, BA3BI2, BA2PB, BA3SB2, BI2CA3, CA3SB2, CASE, CA2SN, K2SE AND NIAL. 